• Major surgery can lead to postoperative disturbances in sleep patterns with subjective deterioration of sleep quality according to patients' reports as well as objective alterations of sleep architecture, as recorded by polysomnography
• Factors implicated in postoperative sleep disturbances include but are not limited to the severity of the surgical procedure, the neuroendocrine response to surgery, inadequate treatment of postoperative pain and external factors interfering with sleep, such as light, noise and therapeutic procedures
• There are differences in the molecular mechanisms inhalational anesthetics and intravenous agents affect different brain regions to induce anesthesia. Our hypothesis is that these differences may also be evident during the postoperative period, affecting brain functions which are involved in postoperative sleep architecture. So, the aim of this study will be to assess the effect of two different anesthetic techniques (propofol versus desflurane) of maintaining general anesthesia in patients subjected to similar major operations
• Patients will be assessed with the Pittsburgh Sleep Quality Questionnaire (PSQI), regarding preoperative and long term postoperative sleep quality, sleep diaries regarding early postoperative sleep quality and biochemical markers (cortisol, prolactin and melatonin) regarding neuroendocrine response to surgery and disturbances in endogenous circadian secretion associated with sleep

• Major surgery can lead to postoperative disturbances in sleep patterns with subjective deterioration of sleep quality according to patients' reports as well as objective alterations of sleep architecture, as recorded by polysomnography
• These disturbances include severe sleep fragmentation, rapid eye movement (REM) and slow wave sleep significant reductions in duration as well as an increase in non-REM sleep stages. Spontaneous awakenings are also frequently reported
• After the third or fourth postoperative day, there is a substantial rebound in total REM activity, with frequent reports of vivid nightmares
• Factors implicated in postoperative sleep disturbances include but are not limited to the severity of the surgical procedure, the neuroendocrine response to surgery, inadequate treatment of postoperative pain and external factors interfering with sleep, such as light, noise and therapeutic procedures
• There are differences in the molecular mechanisms inhalational anesthetics and intravenous agents affect different brain regions to induce anesthesia. Our hypothesis is that these differences may also be evident during the postoperative period, affecting brain functions which are involved in sleep architecture, since sleep is an altered state of consciousness like anesthesia. So, the aim of this study will be to assess the effect of two different anesthetic techniques of maintaining general anesthesia in patients subjected to similar major operations
• Patients taking part in the study will be evaluated regarding their preoperative sleep quality by the Pittsburgh Sleep Quality Questionnaire (PSQI). The PSQI examines seven components of sleep quality retrospectively over a period of four weeks: subjective sleep quality, sleep latency, sleep duration, habitual sleep efficiency, sleep disturbances, use of sleeping medication, and daytime dysfunction over the last month. The patient self-rates each of these seven areas of sleep. Scoring of answers is based on a 0-3 scale, whereby '3' reflects the negative extreme on the Likert scale. The global score is generated by summing up all seven component scores and ranges from 0 to 21, with higher values corresponding to reduced sleep quality.
• Consequently, patients will be randomized to one of two groups: one group with general anesthesia maintenance based on an intravenous agent (propofol) and a second group with general anesthesia maintenance based on an inhalational agent (desflurane)
• Patients will be assessed postoperatively with sleep diaries regarding potential sleep disturbances while they will be subjected to a long-term assessment of sleep quality by the use of the PSQI one and three months postoperatively
• Since anesthetic-related differences in hormone profiles are expected, markers related to the neuroendocrine response to stress (cortisol, prolactin) will also be assessed to investigate differences between the two different anesthetic regimes
• Impaired melatonin secretion has been proposed as one of the mechanisms involved in postoperative sleep disturbances. It is therefore expected that different methods of anesthetic maintenance may affect the endogenous circadian melatonin rhythm in a different way. Consequently, melatonin secretion will also be measured to investigate potential desynchronization of melatonin rhythm as well as differences in melatonin secretion between the two different anesthetic techniques
• The clinical implications of this study lie in the fact that postoperative sleep disturbances can lead to postoperative hemodynamic instability, episodic hypoxemia and mental status deterioration, which can all untowardly affect the short and long-term postoperative outcome. It would be interesting to determine whether one of the two anesthetic regimes is superior to the other as far as postoperative disturbances in sleep architecture are concerned

Inclusion Criteria:

• Adult patients, American Society of Anesthesiologists (ASA) distribution I-III, scheduled for elective upper major abdominal surgery

Exclusion Criteria:

• Alcoholism
• Mental disability
• Psychiatric disease (depression, dementia)
• Preoperative use of sleeping medication